Electric Current, Circuits, Electric Current, Circuits, Resistance and Ohm’s lawResistance and Ohm’s law

MHR pg. 619-632MHR pg. 619-632

What is Electric Current?What is Electric Current?

An electric current is:An electric current is:

the movement of electrons ( think of a the movement of electrons ( think of a water current- movement of water)water current- movement of water)

These electrons carry energy ( in volts) These electrons carry energy ( in volts) and can transfer their energy to a load and can transfer their energy to a load such as a light bulbsuch as a light bulb

Formula for CurrentFormula for Current

I = Q / I = Q / ΔΔtt

Where Where

I = current ( amps)I = current ( amps)

Q = amount of charge ( coulombs)Q = amount of charge ( coulombs)

ΔΔt = change in time ( seconds)t = change in time ( seconds)

Problem #1: Cell phone chargersProblem #1: Cell phone chargers

What is the current travelling through a cell What is the current travelling through a cell phone charger when 0.20 mC of electrons phone charger when 0.20 mC of electrons pass a point in 0.75 min?pass a point in 0.75 min?

Answer:Answer:

4.4 x 10 4.4 x 10 -6-6 A A

How do you measure electric current?How do you measure electric current?

Review.Review.

What is going on with the diagram below?What is going on with the diagram below?

Where would you put the ammeter?Where would you put the ammeter?

Follow the symbols pg. 619 in your text bookFollow the symbols pg. 619 in your text book

How bright are the two light bulbs?

Analyse this circuit:Analyse this circuit:

The ammeter goes ______the first light bulb.

How bright are the two light bulbs?

How much energy does each light How much energy does each light bulb absorb?bulb absorb?

Measure the voltage ( change in energy) Measure the voltage ( change in energy) across each light bulb in the circuit below:across each light bulb in the circuit below:

The light bulb that is brighter has more or less energy?

How much energy does each light How much energy does each light bulb absorb?bulb absorb?

Measure the voltage ( change in energy) Measure the voltage ( change in energy) across each light bulb in the circuit below:across each light bulb in the circuit below:

How bright are the light bulbs? How much energy does each light bulb require?

Electrical Resistance (R)Electrical Resistance (R)

Electrical Resistance: is a measure of Electrical Resistance: is a measure of how difficult it is for an electrical current to how difficult it is for an electrical current to travel through a materialtravel through a material

High resistance materials: do not allow an High resistance materials: do not allow an electric current to pass through ( example: electric current to pass through ( example: plastic)plastic)

Low resistance materials: allow electric Low resistance materials: allow electric current to pass through ( example: copper)current to pass through ( example: copper)

ResistorResistor

An electrical device An electrical device that has a specific that has a specific resistanceresistance

The units for resistor The units for resistor is ohms or is ohms or ΏΏ

Ohm’s LawOhm’s Law

If you were to graph If you were to graph the amount of energy the amount of energy the electrons transfer the electrons transfer to a load (V) vs the to a load (V) vs the flow of electrons that flow of electrons that pass through a load pass through a load (I), the graph would (I), the graph would look like this:look like this:

So what do we do with straight lines?So what do we do with straight lines?

Take their slope!!!!Take their slope!!!!

Ohm’s LawOhm’s Law

Where :Where :

R= resistance ( R= resistance ( ΏΏ))

V = potential V = potential difference ( V)difference ( V)

I = current ( A)I = current ( A)

Your Turn…Your Turn…

Read pg. 622-625Read pg. 622-625

MHR pg. 632 # 21-26 ( blue background)MHR pg. 632 # 21-26 ( blue background)

MHR pg. 632 # 1,2 ( yellow background)MHR pg. 632 # 1,2 ( yellow background)